Sound reproduction system



March 8, 1966 w. A. MURRAY SOUND REPRODUCTION SYSTEM 2 Sheets-Sheet 1Filed Nov. 1, 1963 I M w O k H v. h

Km 87 u W INVENTOR. WILLARD A. MURRAY Maw WM Mfume. s

United States Patent 3,239,028 SOUND REPRODUCTION SYSTEM Willard A.Murray, 3920 La Salle Court, Apt. 185,

' Indianapolis, Ind. Filed Nov. 1, 1963, Ser. No. 321,394 '7 (Ilaims.(Cl. 18131) This is a continuation-in-part of my US. application SerialNo. 244,157, filed December 12, 1962, now abandoned.

This invention relates generally to sound reproduction systems orapparatus and in particular to a speaker assembly for reproducingrecorded music or the like, the assembly being characterized by itsrelatively small size, clean, balanced reproduction over a wide range offrequencies and substantially omnidirectional propagation or radiationof sound.

Conventional speaker systems used in high fidelity reproduction of soundinvariably utilize at least two speakers or transducers, more oftenthree or more. For good audible reproduction of a large range offrequencies, with the lower end of the range extending to or near cyclesper second, these conventional speaker systems require relatively largeenclosures, careful placement of the enclosures within a room andattention to the acoustic properties of the room. Even with carefulattention to these details, the results leave much to be desired and theaesthetic problem in fitting the relatively large enclosure into whatmay be the rigid, period decor of the room remains.

The speaker system of the present invention utilizes only a singlespeaker or transducer which may be of the conventional, inexpensive conetype of small diameter. Because of the enclosure construction, the sizeof the enclosure may be quite small, of the order of 8 /2 X 11 X 2inches and thus can be unobtrusively located within a room. Placement ofthe speaker system within a room is in no sense critical, radiation ofsound is substantially omnidirectional, and no standing waves, producingaudible discontinuities, are set up even in rooms which lack soundattenuating drapes or the like.

It is the primary object of the present invention to provide a speakersystem or apparatus which accomplishes balanced, wide frequency rangesound reproduction while utilizing a relatively small enclosure.

It is a further object of the present invention to provide a speakersystem of the type referred to which utilizes but a single transducer orsound source.

It is a further object of the present invention to provide a speakersystem of the type referred to in which the enclosure is braced so as toprevent loss of energy through movement of the enclosure walls(breathing of the enclosure) when the system is in operation and tocontrol the resonant frequency of the enclosure.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings, wherein:

FIG. 1 is a longitudinal sectional view of one embodiment of the presentinvention;

FIG. 2 is a perspective view of a second embodiment of this invention;

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FIG. 3 is a front elevation substantially to scale of anotherembodiment;

FIG. 4 is a longitudinal sectional view of the embodiment of FIG. 3substantially to scale; and

FIG. 5 is a top plan view, partially broken away and sectioned forclarity, of the embodiment of FIG. 3, and is substantially to scale.

Referring to the drawings, the vibratory body or enclosure 10 is ofgenerally rectangular box configuration having members 11 and 12 formingfront and rear enclosure faces, respectively. Upper and lower ends orpanels 13 and 1d are rigidly joined to the members 11 and 12 and sidepanels (only one of which identified at 16 is visible in the drawing)complete the enclosure. In addition to being rigidly secured by glue,screws or other suitable means at the panel joints, a tension member 17extends transversely across the enclosure and may take the form of a rodthreaded at each end, extending through apertures in the members 11 and12 and receiving, exteriorly of the enclosure, nuts which may betightened to thereby place the member 17 under tension and to deform themembers 11 and 12 inwardly somewhat so that they present a slightlyconvex surface to the interior of the enclosure.

The front face member 11 of the enclosure is provided with a frontradiation aperture 18 and rigidly mounted over the aperture 18 is aconventional transducer which includes a vibratory element and hereinshown as taking the form of a conventional diaphragm or cone typespeaker identified generally at 19. The face member 11 also has formedtherein an aperture or orifice 21. A bafiie 22 is rigidly mounted on theinner face of the member 11 and extends contiguously with the sidepanels to a point adjacent the rear face of the member 12 therebyproviding an elongated orifice 23 The 'bafiie member 22 divides theinterior of the enclosure into an upper portion 24 and a lower portion26.

Spacers 27 rigidly support a plate 253 which overlies both the aperture18 and the orifice 21, the plate 28 and the adjacent front face of theenclosure proper defining a space or chamber indicated at 29, thischamber 29 having a peripheral edge portion 2% which is open. Aspreviously mentioned, the size of the enclosure may be of the order of 8/2 x 11 x 2 inches.

The presence of the chamber 24 provides an acoustic stiffness againstwhich the transducer diaphragm must move and this acoustic stiffnessseen" by the diaphragm is transferred, under control of the orifice 23,into the chamber 26. This stiffness is transformed by means of thevolume of the chamber 26 and the duct 21 into high amplitude radiationat the mouth of the duct 21. The plate 28 acts as an acoustic lensserving to disperse the sound to the room in a substantiallyomnidirectional pattern. The mass of air in the space or chamber 29,that is, the mass vibrated by front radiation from the speaker 19 andfrom the port 21 also serves, in acting on the front of the speakerdiaphragm, to balance the air load in the chamber 24 at the rear of thediaphragm. Vibration of the mass of air in the chamber 29 further isutilized to excite vibration in the plate 28 for the purpose ofreinforcing any desired frequency range depending upon the size andmaterial from which the plate 28 is formed. Substantially any frequencyrange may be reinforced as desired, it being only necessary to choosethe correct material and size for the plate 28. It will be understoodthat several superposed spaced-apart parallel plates 28 may be used inplace of a single plate 28 if several frequency ranges are to bereinforced. These several plates 28 would be fixedly mounted on eachother the same as plate 28 is mounted on front wall ill.

FIG. 2 shows an enclosure having a modified exterior configuration. Thisstructure is provided with the interior member (not shown) dividing theenclosure into two chambers with an orifice communicating therebetween.A front radiation aperture 41 is provided comparable to aperture 15; inFIG. 1. The face member 42 is also provided with a plurality of orificesor ports 43. A plate 44 is rigidly supported by spacers 46, and overliesboth the aperture 41 and the orifices 43, the plate and the adjacentface member 42 defining a chamber comparable in function to the chamber29 of FIG. 1.

The structure of the present invention, in addition to the advantagespointed out above, also is characterized by a transient response whichis substantially faster than that of conventional speaker systemsbecause of the low inertia or capacitance of the present system due toits relatively small size.

Another embodiment of this invention is illustrated in FIGS. 3, 4 and 5which are drawn substantially to scale. In these figures, like parts areindicated by like numerals with the suffix 11" being added thereto. Inthis embodiment, the tensioning element 17a is preferably an ordinaryround-headed screw having a head 48 bearing against the outer surface ofthe midportion of the rear wall or panel 12a and a nut 50 thereon whichbears against the outer surface of the midportion of the front wall orpanel 11a. As shown, the nut 50 is threaded downwardly sufficiently tobow and tension the two walls 11a and 12a inwardly toward each other.The exact amount of bowing or curving is determined by all of thedimensions and parameters of the various components which make up thetotal apparatus, the speaker 1% being one such component. Alteration ofthe degree of bowing or tensioning serves to modify the resonance andradiation characteristics of the apparatus. In the final analysis, thesewalls 11a and 12a will be tensioned or bowed to an extent as determinedby the response or radiation characteristics desired in the finaldesign.

The speaker 19a is eccentrically mounted with respect to the smallerspeaker opening 18a as shown more clearly in FIGS. 3 and 4. The fourspacers 27a, which are preferably formed of wooden dowels, are locatedat the corner portions of the panel 28a and the front wall 11a as shown.These spacers 27a are securely fixed to the panel 28a and wall 11a bysome suitable means such as by glue or screws, or both.

Instead of using a single aperture 21 as shown in FIG. 1, thisembodiment uses two such apertures 21a which are spaced apart as shown.The sizes of these apertures 21 and 21a may be one-half inch to one inchin diameter depending on the results desired.

In the following are given dimensions and parameters of the embodimentof FIGS. 3-5 which is capable of reproducing music with high degree offidelity. These dimensions are given by way of example only and are notto be considered as restrictive of the scope of the invention.

In this working embodiment, the walls 11a, 12a and the panel 28a aremade of three-ply sheets of walnut plywood one-fourth inch thick, andthe cabinet ends 13a, 14a and the cabinet sides 26a and 26b are made ofthreefourths inch thick walnut hardwood. As shown more clearly in FIGS.4 and 5, the ends and sides of the cabinet are rigidly secured togetherby gluing and the like to form a rigid rectangular frame for theapparatus. The edges of this frame are rabbeted to receive and flushmount the front and rear panels Illa and 12a, as shown more clearly inFIGS. 4 and 5. These panels 11a and 12a are securely glued to the frameto provide a rigid enclosure structure.

The dimensions are indicated in FIGS. 3, 4 and 5 by the lower caseletters which are listed in the following,

the actual figures in inches being listed oppositely:

i--5 /2 inches -8 inches k-S inches l-7% inches m-10% inches n3 /zinches a11 inches b5 inches c-4% inches d--8 A2 inches e-3% inches e 2/2 inches ;f /2 inch p2 in. dia. gl% inches r-2 V in. radius lz-2%inches s- /2 inch It is well understood by persons skilled in the artthat different speaker systems have different response and radiationcharacteristics and that when they are used in the reproduction ofmusic, different systems will appeal to diiferent people. An individualdesiring to purchase a speaker system usually will listen to a varietyof differently designed systems before making a selection. Thus, thereis no single response or radiation characteristic which can satisfy alldemands; hence, designs of almost all speaker systems are variedsomewhat to provide different models. With respect to the presentinvention, the sound-reproducing characteristics thereof may be variedby altering any one or more of the parameters given in the preceding.However, the actual working embodiment of the invention as disclosed inconnection with FIGS. 3-5 provides reproduction characteristics whichare generally pleasing in connection with the reproduction of music. Thesound emitted by the speaker @911 is modified by the resonancecharacteristics of the cavity 52 inside the cabinet 10, by the size ofthe aperture 21a, the spac ing of the panel 28a from the front wall 11a,and the materials of the cabinet and panel 28a whereby the sound emittedby the speaker 1% throughout the audible spectrum is reinforced incertain areas and attenuated in others, the total responsecharacteristic being substantially fiat within the definition of thespeaker art. This flatness in response extends from the low regions ofapproximately -100 cycles per second up to the higher regions of from10,000 to 12,000-cycles. This response is acquired even though theenclosure is of miniature size and only a single driver is used therein.

While earlier in the discussion of the embodiment of FIG. 1 it wastheorized that chamber 24 provided acoustic stiffness with the air loadin the chamber being balanced, it should be realized that the presentinvention comprehends an increase in transient response (as compared toprior art systems) which results in a reduction of air load quantitiesand the development of a number of impact areas, these areas havingdifferent impact values (instantaneous pressure).

With respect to directivity of emitted sound, the present invention maybe considered as omnidirectional, or in other words as emitting sound ina spherical pattern. Thus, the present invention may be operated in anyposition, sitting on its end, side, back or the like, or it may beoperated while hung on a wall Without impairing its omidirectionalradiation.

While the invention has been disclosed and described in some detail inthe drawings and foregoing description, they are to be considered asillustrative and not restrictive in character, as other modificationsmay readily suggest themselves to persons skilled in this art withoutdeparting from the scope of this invention as defined by the appendedclaims.

What is claimed is:

1. Sound-reproducing apparatus comprising cabinet means which defines anenclosed cavity, said cabinet means having front and rear wall portions,said front wall portion being provided with a speaker opening and atleast one aperture, a diaphragm speaker mounted within said cavity onsaid front wall portion with the diaphragm over said speaker opening,and panel means spaced from and mounted on said front wall portion onthe side opposite said speaker and defining a chamber therewith having aperipheral edge portion which is open, said panel means over lying saidopening and aperture, said cabinet means being of a vibrationtransferring material; said cavity, said chamber, said opening and saidaperture being of such sizes as will vibrationally couple said diaphragmto said cabinet means to produce omnidirectional radiation of sound bysaid diaphragm, said cabinet means and said panel means as a commonsound source; said sizes also being such as to reduce the amplitude ofvibration of said diaphragm in comparison with that which would beexistent with said speaker operating in the absence of said cabinetmeans.

2. Sound-reproducing apparatus comprising cabinet means which defines anenclosed cavity, said cabinet means having front and rear wall portions,said front wall portion being provided with a speaker opening and atleast one aperture, a diaphragm speaker mounted within said cavity onsaid front wall portion with the diaphragm over said speaker opening,and panel means spaced from and mounted on said front wall portion onthe side opposite said speaker and defining a chamber therewith having aperipheral edge portion which is open, said panel means overlying saidopening and aperture, said chamber as defined by said panel means andsaid front wall portion being substantially flat and opening radiallyoutwardly through said edge portion beyond said cabinet means, saidcabinet means being of a vibration-transferring material; said cavity,said chamber, said opening and said aperture being of such sizes as willvibrationally couple said diaphragm to said cabinet means to produceomnidirectional radiation of sound by said diaphragm, said cabinet meansand said panel means as a common sound source; said sizes also beingsuch as to reduce the amplitude of vibration of said diaphragm incomparison with that which would be existent with said speaker operatingin the absence of said cabinet means.

3. Sound-reproducing apparatus comprising cabinet means having spacedapart first and second Wall portions and defining an enclosed cavity,said wall portions being self-supporting and vibratory at frequencieswithin the audible spectrum, means rigidly interconnecting the centralportions of said wall portions together, a speaker opening and anaperture in said first wall portion, 21 diaphragm speaker mounted withinsaid cavity on said first wall portion with said diaphragm over saidspeaker opening, and panel means spaced from and mounted on said firstwall portion on the side opposite said speaker and defining a chambertherewith having a peripheral edge portion which is open, said chamberhaving substantially unobstructed communication with the surroundingatmosphere in a direction radially outwardly beyond said edge, saidpanel means overlying said opening and aperture, said panel means beingvibratory at predetermined frequencies within the spectrum of audiblefrequencies; said cavity, said chamber, said aperture and said openingbeing of such sizes as will vibrationally couple said diaphragm to saidcabinet means to produce omnidirectional radiation of sound by saiddiaphragm, said cabinet means and said panel means as a common soundsource; said sizes being such as to reduce the amplitude of vibration ofsaid diaphragm in comparison with that which would be existent with saidspeaker operating in the absence of said cabinet means.

4. Sound-reproducing apparatus comprising cabinet means having spacedapart first and second wall portions and defining an enclosed cavity,said wall portions being self-supporting and vibratory at frequencieswithin the audible spectrum, means rigidly interconnecting the centralportions of said wall sections together and also for applying forces tosaid central portions which curve said wall portions inwardly towardeach other, a speaker opening and a radiating aperture in said firstwall portion, a diaphragm speaker mounted within said cavity on saidfirst wall portion with said diaphragm over said speaker opening, andpanel means spaced from and mounted on said first wall portion on theside opposite said speaker and defining a chamber therewith having aperipheral edge portion which is open, said chamber having substantiallyunobstructed communication with the surrounding atmosphere in adirection radially outwardly beyond said edge, said panel meansoverlying said opening and aperture, said panel means being vibratory atpredetermined frequencies within the spectrum of audible frequencies;said cavity, said chamber, said aperture and said opening being of suchsizes as will vibrationally couple said diaphragm to said cabinet meansto produce omnidirectional radiation of sound by said diaphragm, saidcabinet means and said panel means as a common sound source; said sizesbeing such as to reduce the amplitude of vibration of said diaphragm incomparison with that which would be existent with said speaker operatingin the absence of said cabinet means.

5. A sound-reproducing apparatus comprising a cabinet which defines anenclosed cavity, said cabinet being of rectangular shape and havingopposite front and rear walls, two ends and two sides, said front andrear walls being of substantially the same area which is larger than thearea of said ends and sides, said walls, sides and ends being securelyfixed together, a speaker opening provided in one end portion of saidfront wall, at least one radiating aperture provided in the opposite endportion of said front wall and spaced from said speaker opening, aconetype loudspeaker of larger diameter than said speaker openingdisposed in said cavity and mounted on said front wall with the coneover said speaker opening, said speaker being disposed eccentricallywith respect to said speaker opening, said ends and sides having greaterrigidity than said walls, a rigid rod-like element having opposite endssecured to the opposite central portions of said walls, respectively,and forcing said central portions inwardly toward each other by apredetermined amount, a flat rigid panel which is vibratory atpredetermined frequencies in the audio spectrum, said panel being ofsubstantially the same size and shape as said front wall and congruentlymounted on the latter in parallel spaced relation therewith, four rigidspacing elements securing said panel to said front Wall at the fourcorner portions of the latter, said panel overlying said speaker openingand said aperture, said front and rear walls and said panel beingvibratory at predetermined frequencies in response to sounds emitted bysaid speaker, the sizes of said speaker opening, aperture, cavity,spacing of said panel from said front wall, and the inward force exertedon said front and rear walls being such as to reduce the amplitude ofthe vibration of said cone in comparison with that which would beexistent with said speaker operating alone in the absence of saidcabinet.

6. The apparatus of claim 5 wherein said cabinet and panel are flat andof hardwood.

7. The apparatus of claim 5 wherein said cavity has dimensions ofapproximately nine and one-half inches in length, three inches in depthand six and one-half inches in width, said speaker opening being twoinches in diameter, said aperture one-half to one inch in diameter, thespacing of said panel from said front wall one-half inch, said walls andpanel being hardwood one-fourth inch thick.

(References on following page) References Cited by the Examiner UNITEDSTATES PATENTS Kressmann 181-31 Nicolson 18131 Evans 181-31 Bilhuber181-31 Wenzel 181-31 Tavares 181-31 Wildman 18131 10 Lowell, 181-31FOREIGN PATENTS 1/1961 Austria. 2/1930 France. 4/1932 Great Britain. 2/1958 Italy.

LEO SMILOW, Primary Examiner.

1. SOUND-REPRODUCING APPARATUS COMPRISING CABINET MEANS WHICH DEFINES ANENCLOSED CAVITY, SAID CABINET MEANS HAVING FRONT AND REAR WALL PORTIONS,SAID FRONT WALL PORTION BEING PROVIDED WITH A SPEAKER OPENING AND ATLEAST ONE APERTURE, A DIAPHRAGM SPEAKER MOUNTED WITHIN SAID CAVITY ONSAID FRONT WALL PORTION WITH THE DIAPHRAGM OVER SAID SPEAKER OPENING,AND PANEL MEANS SPACED FROM AND MOUNTED ON SAID FRONT WALL PORTION ONTHE SIDE OPPOSITE SAID SPEAKER AND DEFINING A CHAMBER THEREWITH HAVING APERIPHERAL EDGE PORTION WHICH IS OPEN, SAID PANEL MEANS OVER LYING SAIDOPENING AND APERTURE, SAID CABINET MEANS BEING OF A VIBRATIONTRANSFERRING MATERIAL; SAID CAVITY, SAID CHAMBER, SAID OPENING AND SAIDAPERTURE BEING OF SUCH SIZES AS WILL VIBRATIONALLY COUPLE SAID DIAPHRAGMTO SAID CABINET MEANS TO PRODUCE OMNIDIRECTIONAL RADIATION OF SOUND BYSAID DIAPHRAGM, SAID CABINET MEANS AND SAID PANEL MEANS AS A COMMONSOUND SOURCE; SAID SIZES